sqlalchemy.ext.declarative.ConcreteBase

A helper class for 'concrete' declarative mappings. :class:`.ConcreteBase` will use the :func:`.polymorphic_union` function automatically, against all tables mapped as a subclass to this class. The function is called via the ``__declare_last__()`` function, which is essentially a hook for the :meth:`.after_configured` event. :class:`.ConcreteBase` produces a mapped table for the class itself. Compare to :class:`.AbstractConcreteBase`, which does not. Example:: from sqlalchemy.ext.declarative import ConcreteBase class Employee(ConcreteBase, Base): __tablename__ = 'employee' employee_id = Column(Integer, primary_key=True) name = Column(String(50)) __mapper_args__ = { 'polymorphic_identity':'employee', 'concrete':True} class Manager(Employee): __tablename__ = 'manager' employee_id = Column(Integer, primary_key=True) name = Column(String(50)) manager_data = Column(String(40)) __mapper_args__ = { 'polymorphic_identity':'manager', 'concrete':True} The name of the discriminator column used by :func:`.polymorphic_union` defaults to the name ``type``. To suit the use case of a mapping where an actual column in a mapped table is already named ``type``, the discriminator name can be configured by setting the ``_concrete_discriminator_name`` attribute:: class Employee(ConcreteBase, Base): _concrete_discriminator_name = '_concrete_discriminator' .. versionadded:: 1.3.19 Added the ``_concrete_discriminator_name`` attribute to :class:`_declarative.ConcreteBase` so that the virtual discriminator column name can be customized. .. versionchanged:: 1.4.2 The ``_concrete_discriminator_name`` attribute need only be placed on the basemost class to take correct effect for all subclasses. An explicit error message is now raised if the mapped column names conflict with the discriminator name, whereas in the 1.3.x series there would be some warnings and then a non-useful query would be generated. .. seealso:: :class:`.AbstractConcreteBase` :ref:`concrete_inheritance`